fix ftguess unittests for windows

hard-coded "/" directory separator

tests/ftguess/test_basic.py

@@ -109,7 +109,7 @@ def test_encoding(self):
         """Check whether text file encoding is detected correctly"""
         n_matches = 0
         for filename, file_contents in loop_over_files(subdir='basic'):
-            match = re.match(r'basic/test-sample-(ascii|latin1|utf[816_lbe]+)(?:-nobom|-withbom)?.txt', filename)
+            match = re.match(r'basic.test-sample-(ascii|latin1|utf[816_lbe]+)(?:-nobom|-withbom)?.txt', filename)
             if not match:
                 continue
             n_matches += 1